[libvirt] Strange failure of commandtest when doing F15 build

Today I added some patches to the f15 branch of Fedora libvirt, ran
"fedpkg local" to be sure it was all in order, then did a "fedpkg commit
-p" and "fedpkg build". When I came back awhile later, I found that it
had failed. Looking in the logs, I could see that the failure was due to
tests/commandtest.
Since the failure says almost nothing (and there was nothing even
remotely related in any of the changes), I decided to try and build 1)
the older libvirt and 2) with debugging turned on in the tests.
I had no idea how to do this, but nirik in #fedora-devel helped me out,
and I did the following:

1) reverted the libvirt.spec file locally (so that I'm working with
source that previously built)

2) added the following lines just prior to "make check" in the specfile:
export VIR_TEST_VERBOSE=1
export LIBVIRT_LOG_OUTPUTS=3:stderr
export LIBVIRT_LOG_FILTERS="1:command"
export VIR_TEST_DEBUG=2
3) added something identifiable to the version string in libvirt.spec:
Release: 4.test%{?dist}%{?extra_release}
4) fedpkg srpm
5) koji build --scratch dist-f15 libvirt-0.8.8-4.test.fc15.src.rpm
This build also failed. The results are here:
http://koji.fedoraproject.org/koji/taskinfo?taskID=3182099
(search for "... FAIL")
So it appears that some other package on the build machine has been
updated, and it's causing most of the tests in commandtest to fail.
Unfortunately, even when debugging is turned on the tests don't say
anything about why they failed.
Any ideas?